best antenna

[STR_EDDS]

i have a question.
should i measure bevor the bend or in the middle of the curve?

its 1-2mm extra, depends where i measure...
hope you understand what i mean

qeafsdyx.png

[abcd567]

i have a question.
should i measure bevor the bend or in the middle of the curve?

its 1-2mm extra, depends where i measure...
hope you understand what i mean

[ATTACH=CONFIG]5385[/ATTACH]

Distances are from center of stub wire, not from center of stub.
I feel the diagram below replies to your question.
What is the diameter (in mm or AWG) of wire you are using?
Wie weit sind Sie von flughafen Stuttgart?
franklin-1mm to 3mm dia wire-4mm fold-5mm stub-how-to-R2.jpg

[delcomp]

If I was building the Antenne,. I would understand it as... :
Antenne.jpg

[STR_EDDS]

Distances are from center of stub wire, not from center of stub.
I feel the diagram below replies to your question.
What is the diameter (in mm or AWG) of wire you are using?
Wie weit sind Sie von flughafen Stuttgart?
[ATTACH=CONFIG]5394[/ATTACH]

i use 1,5mm² wire.
My distance to EDDS is 15 kilometers.

Here is my latest prototype from yesterday.
The antenne plott is a combination of 2 pictures.
white planes are the planes that i receive, yellow ADB-S on FR24.
Reception is very unstable with this one, i have to build a new one

How do i match the antenna? Move the adaption sideways an watch if i get more planes?

IMG_20150109_221443.jpg123.jpg

[abcd567]

i use 1,5mm² wire.
My distance to EDDS is 15 kilometers.

Here is my latest prototype from yesterday.
The antenne plott is a combination of 2 pictures.
white planes are the planes that i receive, yellow ADB-S on FR24.
Reception is very unstable with this one, i have to build a new one

How do i match the antenna? Move the adaption sideways an watch if i get more planes?

[ATTACH=CONFIG]5398[/ATTACH][ATTACH=CONFIG]5399[/ATTACH]

(1) Yes, move the Coax tap, in steps of 2 mm to left & right and judge by maximum range, number of packets and number of planes. It is a tedious process.
(2) The impedance matching is very dependent on the gap between stub wires of IMPEDANCE MATCHING STUB (the stub in the middle). It looks from your photo that the gap is very big, about 10mm from surface of wire to surface of wire. You wont be able to get good SWR and hence good performance with this big gap.
(3) The gap in my sketch is "5mm center of wire to center of wire". The "surface of wire to surface of wire gap" works out to be:
Surface to surface gap = center to center gap - d/2 -d/2 = center to center gap -d
For 5 mm center to center gap, surface to surface gap = 5mm - 1.5mm = 3.5mm. Please see sketch below

By the way, nice to see your triangular scale. Few people use it, but it is a nice piece of instrument. Long ago I had one made by Faber-Castell.

stub wire spacing 1.PNG

franklin-fold 4mm-stub variable-sweep swr 1.PNG

[abcd567]

@STR_EDDS:
Please see the photos of my Franklin below. The coax tap arrangement uses a terminal block. The spacing of screws in terminal block is 5mm center to center, which automatically keeps the spacing of stub wires 5mm center to center. The optimum center to center spacing is 3mm, which using a 1.5mm dia wire results in surface to surface gap of 3mm-1.5mm=1.5mm, difficult to make.

I used to slide the terminal block in 2mm steps to determining its optimum position by trial and error.

DSC03054R.jpg . DSC03055R.jpg

[abcd567]

@STR_EDDS:
Forum Member "trigger" had put up lot of effort & trials and has finally succeedded in making a good Franklin. He may help you with tips & photos.

@trigger:
Hi Dave, hope with your valuable experience in making a successful Franklin, you can provide good help to our new member STR_EDDS.

[STR_EDDS]

ok thanks, now i have all information to build a good antenna.
i will post progress here.

[abcd567]

Hi all. Typing this message from my first Pi (R Pi B+) on it's maiden boot.

[gquejada]

Distances are from center of stub wire, not from center of stub.
I feel the diagram below replies to your question.
What is the diameter (in mm or AWG) of wire you are using?
Wie weit sind Sie von flughafen Stuttgart?
[ATTACH=CONFIG]5394[/ATTACH]

Hi, abcd567!
Using these Illustrated Steps for the Franklin, may I CUT and then SOLDER the wires instead of just bending them? With a small file, I could get the required lengths and especially the spacings in mm, as required...

[SpaxmoidJAm]

yes that will work, it will however be a little more fragile, but easy to fix and tune.

[STR_EDDS]

maybe it is stupid, but can this one work?

rwegdfsvc.png

[abcd567]

Hi, abcd567!
Using these Illustrated Steps for the Franklin, may I CUT and then SOLDER the wires instead of just bending them? With a small file, I could get the required lengths and especially the spacings in mm, as required...

Yes it will work, but will make antenna mechanically weak.

It is much easier to drill a hole in a piece of wood by a 4mm or 3mm dia drill, leave the drill bit half way inside the hole, and bend the wire around it (or hold the drill bit in a bench vice, and bend the wire around it).

Alternatively you can use a 4mm or 3mm dia bolt driven into a piece of wood (or held in a bench vice), and bend the wire around it.

You can also use a 3mm or 4mm thick plastic or wooden sheet and bend the wire over sheet's edge. I remember this method was used by forum member "trigger".

[abcd567]

maybe it is stupid, but can this one work?

[ATTACH=CONFIG]5410[/ATTACH]

Your attempt to make a new design is not stupid. I like and appreciate your desire to improve & like your creativity.

Unfortunately, this design will give ZERO output signal.
You have four pairs of parallel wires in your design. The currents induced by Radio Waves in each pair of parallel wires have same direction & magnitude, hence cancel each other, resulting in zero output. So the four pairs will give 0+0+0+0=0

In the Franklin antenna, the hairpins (stubs) are made of parallel wires, and therefore their net pickup of Radio Waves is zero.
It is the single vertical half-wave (138mm) wires which contribute to output of the antenna.

Then why the Franklin has hairpins (stubs)?
All stubs (except middle one) serve to match the phases of currents in adjacent half-wave single-wire sections.
The middle one has a special function: Matching the high impedance of antenna (several hundred ohms) to low impedance of coax cable (75 ohms).

Do not get discouraged by what I have written. continue with your creativity. Many new inventions & successful designs were done by novices & hobbyists. What you need is a little theoretical knowledge which you can easily get by searching & browsing the web.

[abcd567]

Using my first RPi connected to TV flashed back my memory to 1970's/1980's, when Sinclair and Commodore 64 computers used TV as monitors.